/* -------------------------------------------------------------------------
 *
 * timer.c
 *    Microsoft Windows Win32 Timer Implementation
 *
 *    Limitations of this implementation:
 *
 *    - Does not support interval timer (value->it_interval)
 *    - Only supports ITIMER_REAL
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/backend/port/win32/timer.c
 *
 * -------------------------------------------------------------------------
 */

#include "postgres.h"
#include "knl/knl_variable.h"

#include "libpq/pqsignal.h"

/* Communication area for inter-thread communication */
typedef struct timerCA {
    struct itimerval value;
    HANDLE event;
    CRITICAL_SECTION crit_sec;
} timerCA;

static timerCA timerCommArea;
static HANDLE timerThreadHandle = INVALID_HANDLE_VALUE;

/* Timer management thread */
static DWORD WINAPI pg_timer_thread(LPVOID param)
{
    DWORD waittime;

    Assert(param == NULL);

    waittime = INFINITE;

    for (;;) {
        int r;

        r = WaitForSingleObjectEx(timerCommArea.event, waittime, FALSE);
        if (r == WAIT_OBJECT_0) {
            /* Event signalled from main thread, change the timer */
            EnterCriticalSection(&timerCommArea.crit_sec);
            if (timerCommArea.value.it_value.tv_sec == 0 && timerCommArea.value.it_value.tv_usec == 0)
                waittime = INFINITE; /* Cancel the interrupt */
            else {
                /* WaitForSingleObjectEx() uses milliseconds, round up */
                waittime =
                    (timerCommArea.value.it_value.tv_usec + 999) / 1000 + timerCommArea.value.it_value.tv_sec * 1000;
            }
            ResetEvent(timerCommArea.event);
            LeaveCriticalSection(&timerCommArea.crit_sec);
        } else if (r == WAIT_TIMEOUT) {
            /* Timeout expired, signal SIGALRM and turn it off */
            pg_queue_signal(SIGALRM);
            waittime = INFINITE;
        } else {
            /* Should never happen */
            Assert(false);
        }
    }

    return 0;
}

/*
 * Win32 setitimer emulation by creating a persistent thread
 * to handle the timer setting and notification upon timeout.
 */
int setitimer(int which, const struct itimerval* value, struct itimerval* ovalue)
{
    Assert(value != NULL);
    Assert(value->it_interval.tv_sec == 0 && value->it_interval.tv_usec == 0);
    Assert(which == ITIMER_REAL);

    if (timerThreadHandle == INVALID_HANDLE_VALUE) {
        /* First call in this backend, create event and the timer thread */
        timerCommArea.event = CreateEvent(NULL, TRUE, FALSE, NULL);
        if (timerCommArea.event == NULL)
            ereport(FATAL, (errmsg_internal("could not create timer event: error code %lu", GetLastError())));

        errno_t rc = memset_s(&timerCommArea.value, sizeof(struct itimerval), 0, sizeof(struct itimerval));
        securec_check(rc, "\0", "\0");
        InitializeCriticalSection(&timerCommArea.crit_sec);

        timerThreadHandle = CreateThread(NULL, 0, pg_timer_thread, NULL, 0, NULL);
        if (timerThreadHandle == INVALID_HANDLE_VALUE)
            ereport(FATAL, (errmsg_internal("could not create timer thread: error code %lu", GetLastError())));
    }

    /* Request the timer thread to change settings */
    EnterCriticalSection(&timerCommArea.crit_sec);
    if (ovalue != NULL)
        *ovalue = timerCommArea.value;
    timerCommArea.value = *value;
    LeaveCriticalSection(&timerCommArea.crit_sec);
    SetEvent(timerCommArea.event);

    return 0;
}
